Fuel control system

ABSTRACT

A fuel control system for the reheat system of a gas turbine engine which has movable jet-pipe nozzles includes a nozzle position sensing means, a fuel shut-off valve which can be opened only when the nozzles are open and a throttle valve operated by a piston and cylinder unit is acted upon by pressures which are controlled by fluidic control devices and which are derived from air pressures at locations on the engine.

United States Patent Johnson [54] FUEL CONTROL SYSTEM [72] Inventor: Graham Francis Johnson, 26 Bourton Road, Solihull, England [22] Filed: Oct. 28, 1970 [21] Appl. No.: 84,643

[52] U.S. Cl .60/235, 60/237 [51] Int. Cl ..'..F02k 1/18 [58] Field of Search ..60/235, 237

[56] References Cited UNITED STATES PATENTS 2,714,801 8/1955 Sarles ..60/235 2.738,644 3/1956 Alford ..60/235 2,818,703 1/1958 Victor ..60/235 [451 Aug. 15, 1972 3,528,248 9/1970 Cross ..60/235 Primary Examiner-Carlton R. Croyle Assistant Examiner-Robert E. Garrett Attorney-Holman & Stern [57] ABSTRACT A fuel control system for the reheat system of a gas turbine engine which has movable jet-pipe nozzles includes a nozzle position sensing means, a fuel shut-off valve which can be opened only when the nozzles are open and a throttle valve operated by a piston and cylinder unit is acted upon by pressures which are controlled by fluidic control devices and which are derived from air pressures at locations on the engine.

17 Claims, 3 Drawing Figures Patented Aug. 15, 1972 2 Sheets-Sheet 1 i MN INVENTOR ATTORNEYS Patented Aug. 15, 1972 2 Sheets-Sheet 2 4 8 w @5 '73 I I \J \85 i 66 fig i F l G. 3

INVE T09 ATTORNEYS FUEL CONTROL SYSTEM This invention relates to fuel control systems of the type used to govern fuel flow to a gas turbine engine reheat system, in which the said reheat system includes valve means in a fuel supply line between a fuel pump and associated burners, and also includes a jet pipe nozzle which is movable between open and closed positions. The invention has as its object to provide such a control system in a convenient form.

A control system of the type described comprises a nozzle actuating means, a sensing means actuable when the nozzle is in its open position, a valve actuating means responsive to the sensing means, a shut-off valve for the fuel actuable by the valve actuating means, a throttle valve in series with the shut-off valve, a double acting piston and cylinder unit for operating the throttle valve, a switching means operable when the throttle valve moves past a predetermined position to cause the nozzle actuating means to shut the nozzle, a first fluid control means for generating a first control pressure in accordance with the difference between a first reference pressure and an input pressure dependent on a first engine operating condition, the said first control pressure being applied to one side of the piston and cylinder unit, a second fluid control means for generating a second control signal only when the said input pressure is greater than a second reference pressure, a means for generating the first reference pressure in accordance with pressure signals dependent on second, third and fourth engine operating parameters and on the position of the throttle valve, a means for generating the second reference pressure in accordance with pressure signals dependent upon the second, third and fourth engine operating parameters, a third fluid control means responsive to the second control pressure and controlling the pressure applied to the other side of the piston and cylinder unit, the arrangement being such that when the said input pressure is greater than the said second reference pressure, the pressure applied to the said other side of thepiston and cylinder unit is a proportion of the said input pressure, and at all other times is a proportion of the pressure signal which is dependent on the second engine operating parameter and also that, when the said input pressure is greater than the said second reference pressure the throttle valve is in an equilibrium position when the said first control pressure is equal to the said proportion of the input pressure.

A fuel control system in accordance with the invention will now be described by way of example and with reference to the accompanying drawing which shows such a fuel control system diagrammatically.

FIG. 1 shows the system as a whole;

FIG. 2 is a detail ofFlG. l, and

FIG. 3 is a section on line 3-3 in FIG. 2.

In the following description P represents the ambient pressure, P2 and P3 respectively represent the pressures at the exits of the first and second stage compressors and P6 represents the pressure at the jet-pipe outlet of an associated jet engine.

' A jet-pipe nozzle is movable by means which includes a single-acting piston and cylinder unit 10, a double-acting solenoid valve 1 l and plurality of seriesconnected switches 12 in the electrical supply to the valve 11. The double-acting solenoid valve 11 has a closure member 13 operable by a solenoid 14 against a spring 15 to connect either one of passages 16, 17 to an outlet 18 which is at pressure Po. Passages 16, 17 are respectively connected to P3 via restrictors I9, 20. Passage 17 is connected to the cylinder of the unit 10 and passage 16 is connected to a latching means 21 engageable with a nozzle-actuating ram 22 in the unit 10 when the ram 22 is in a position corresponding to nozzle closed, the arrangement being such that the latching means 21 disengages only when there is a high pressure in the passage 16.

Passage 16 is also connected to an inlet of fluidic control device 23 which has a blade 24 movable against a spring 25 by a lever 26 engaged with the ram 22 and which thus provides a means for sensing when the nozzle is fully open. The blade 24 includes an orifice movable into alignment with an axially aligned inlet and outlet of the device 23. The outlet of the device 23 is connected to means for actuating a valve 27, the said means including a servo valve 28 operated by a bellows 67 and a spring-loaded piston and cylinder unit 29. The valve 27 forms a shut-off valve in a fuel line 30. An inlet 31 of the servo valve 28 is connected to the piston and cylinder unit 29 via a passage 32, and to the line 30 via a restrictor 33.

A pressurizing valve 34 is situated downstream of the valve 27 and includes a casing 35, an inlet 36, outlets 37, 38, a pressure connection 39, a sleeve having ports aligned with the outlets 37, 38 and a ported closure member 41. The inlet 36 is connected to the valve 27. The outlet 38 is connected via a restrictor 8 to an outlet 42 of the servo valve 28 and via a line 43 to the vapor gutter (not shown) of the reheat system of the associated engine. The outlet 37 is connected to the fuel gutter of the reheat system. The pressure port 39 is connected via a restrictor to the line 43.

A throttle valve 44 having a restricted by-pass 66 is connected by the line 30 to the valve 27 and by a line 9 to a fuel pump (not shown). The valve 44 has a control member provided with skew grooves and which is rotatable to progressively uncover a plurality of associated parts. A shaft 45 is rotatable by a double-acting piston and cylinder unit 46, via a crank 47, to operate the valve 44. The shaft 45 is rotated in a direction to open the valve 44 by a control pressure P recovered at the outlet of a fluid control means 48, shown in detail in FIGS. 2 and 3.

First and second axially aligned nozzles 70, 71 have respective bores 72,. 73 of frusto-conical form. The bore 72 opens into a chamber 74 within the nozzle 70. The chamber 74 is formed so that the profiles of its walls, viewed along the axis of the nozzle 70, comprise a pair of arcs 75, 76. The centers of the arcs 75, 76 are displaced from each other and from the axis of the nozzle 70.

A pair of passages 77, 78 respective have aligned openings 79, into the chamber 74. The opening 79 is tangential to the are 75, while the opening 80 is displaced from tangency to the arc 76. A further pair of passages 81, 82 have respective openings 83, 84 into the chamber 74. Opening 84 is tangential to the are 76 and opening 83 is displaced from tangency to the are 75. In the example shown the passages 78, 81 are commonly connected, as are the passages 77, 82. The walls of the chamber 74 include flats 85 upon which fluid entering the chamber 74 from the openings 80, 83 will impinge.

When fluid pressure in the passages 77, 82 exceeds that in the passages 78, 81 by a determinable amount, fluid within the chamber 74 rotates as shown by the arrows 86. The rotation of the fluid causes it to emerge from the nozzle 70 in the form of a hollow cone. Substantially none of the fluid pressure will therefore be recovered by the nozzle 71. In all other conditions of fluid pressure in the passages 77, 78, 81, 82 the fluid will not rotate within the chamber 74. In these latter conditions fluid will emerge from the nozzle 70 substantially as a laminar stream, and the greater part of the fluid pressure in the nozzle 70 will be recovered by the nozzle 71.

One of the inputs of the control means 48 is provided by the pressure P6 and the other input by a reference pressure Px obtained from a reference pressure generator 49. The connections to the control means 48 are such that an increase in P6 results in a decrease in P and an increase in Pa: results in an increase in P The generator 49 is effectively a chamber into which pressures P2 and P3 are supplied via restrictors and which has an orifice 50 connected to P and variable by means of a closure member 51 in accordance with the position of the shaft 45, the arrangement being such that closure of the valve 44 results in closure of the orifice 50.

A further fluid control means 52, identical with the control means 48 has as one of its inputs P6 and the other of its inputs a reference pressure Px obtained from a reference pressure generator 53, the connections to the control means 52 being such that a control pressure P0 is obtained in a line 54 only when the pressure P6 exceeds the pressure Px. The pressure generator 53 is generally similar to the generator 49, but no provision is made for varying the orifice connected to P0.

The pressure in line 54 is supplied to a fluid control means 55 which includes a vane 56 operated by a bellows responsive to the pressure Pc. The control means 55 includes aligned ports respectively connected to P2 and to P6 via a restrictor 57 and to a side of the piston and cylinder unit 46 in opposition to that subjected to the pressure P A further port is connected to P0.

The closure member 51 includes a portion 58 adapted to co-act with one switch 59 of the switches 12. The switch 59 is a double-throw switch having a first pair of contacts 60 which are rendered open circuit on actuation of the switch 59, and a second pair of contacts 61 which energize a solenoid 62 to maintain the contacts 60 in an open-circuit condition. The switches 12 also include a switch 63 which is closed when the main throttle of the associated engine is fully open, a switch 64 which is closed when the engine speed is sufficiently high and a switch 65 which is operated to energize the solenoid valve if the switches 59, 63, 64 are already closed.

In use, with the reheat system inoperative the jet pipe nozzle is maintained shut by the latching means 21, the pressure in line 16 being vented to atmosphere via the outlet 18 of the valve 11. If switches 63, 64 and the contacts 60 of the switch 59 are in a closed condition, and switch 65 is subsequently closed, the solenoid valve 11 will be energized. The passage 16 is shut by the closure member 13, whereby the pressure applied to the latching means 21 becomes substantially equal to P3 and the latching means 21 disengages from the ram 22.

The pressure is passage 17 is vented to atmosphere via the outlet 18 and the nozzle opens as a result of aerodynamic forces upon it. When the nozzle is fully open the lever 26 moves the blade 24 so as to align the orifice therein with the inlet and outlet of the control device 23. Pressure P3 is thus applied to the bellows 67 to open the servo valve 28. Fuel thus flows through the by-pass 66, line 30, restrictor 33, valve 28 restrictor 8 and line 43 to the vapor gutter of the reheat system. The resultant pressure drop in the line 32 opens the valve 27 to admit fuel to the pressurizing valve 34. The pressure of the fuel by-passing the throttle valve 44 is sufi'icient only to cause the closure member 41 to open the outlet 38 to provide a further supply of fuel to the vapor gutter.

When the jet-pipe nozzle is opened P6 will fall, and will subsequently rise when the fuel in the vapor gutter is ignited. Prior to ignition P6 will be less than the reference pressure P): supplied by the reference pressure generator 53. There will thus be no pressure in line 54 and the vane 56 in the control means 55 will be withdrawn by the spring action of its associated bellows to allow pressure P2 to be applied to the piston and cylinder unit 46 to maintain the throttle valve 44 shut. After ignition the rise in P6 produces the control pressure Pc which operates on the bellows of the control means 55. The blade 56 then moves so as effectively to shut P2 off from the unit 46 and instead to discharge it through the port to P0. P6 also flows via the restrictor 57 to P0, and the resultant fraction KP of the pressure P6 downstream of the restrictor 57 is applied to the unit 46. The pressure KP is considerably lower than pressure P2. With the throttle valve 44 shut the orifice 50 of the reference pressure generator 49 is also shut. The pressure Px is therefore high and the control pressure P recovered from the control means 48 is correspondingly high. When P6 rises initially after ignition the piston and cylinder unit 46 therefore operates to open the throttle valve 44.

As the flow through throttle valve 44 increases the pressurizing valve 34 opens further to admit fuel to the fuel gutter of the reheat system. The valve 44 continues to open until the consequent reduction in P): causes P to fall to the value of KP Moreover, operation of the reheat system will cause KP to rise. Equilibrium conditions will nevertheless obtain when P equals KP If P6 subsequently rises, KP rises and P falls, the valve 44 closes until Px rises to a value at which the resultant increase in P once again restores equilibrium. 1f P2 or P3 fall, the fall in Px and P closes valve 44 and hence orifice 50 until Px regains a value at which P is equal to KP If KP falls the valve 44 will open until equilibrium is restored.

If the reheat flame is extinguished the pressure P6 will fall, and the valve 44 will open in an attempt to correct this condition. At a predetermined position of the closure member 51 the portion 48 causes the contacts 60 of the switch 59 to open and to de-energize the solenoid valve 11. The jet-pipe nozzle therefore shuts and closes the shut-off valve 27 by means of the control device 23 and the actuating means 28, 29.

If the jet-pipe nozzle closes unexpectedly the shut-off valve will be closed by the valve actuating means substantially as previously described.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A fuel control system for controlling the supply of fuel to burners of a reheat system of a gas turbine engine which includes a jet pipe nozzle movable between open and closed positions, the said fuel control system comprising a nozzle actuating means, a sensing means actuable when the nozzle is in its open position, a valve actuating means responsive to the sensing means, a shut-off valve for the fuel actuable by the valve actuating means, a throttle valve in series with the shut-off valve, a double-acting piston and cylinder unit for operating the throttle valve, a switching means operable when the throttle valve moves past a predetermined position to cause the nozzle actuating means to shut the nozzle, a first fluid control means for generating a first control pressure in accordance with the difference between a first reference pressure and an input pressure dependent on a first engine operating condition, the said first control pressure being applied to one side of the piston and cylinder unit, a second fluid control means for generating a second control signal only when the said input pressure is greater than a second reference pressure, a means for generating the first reference pressure in accordance with pressure signals dependent on second, third and fourth engine operating parameters and on the position of the throttle valve, a means for generating the second reference pressure in accordance with pressure signals dependent upon the second, third and fourth engine operating parameters, a third fluid control means responsive to the second control pressure and controlling the pressure applied to the other side of the piston and cylinder unit, the arrangement being such that when the said input pressure is greater than the said second reference pressure, the pressure applied to the said other side of the piston and cylinder unit is a proportion of the said input pressure, and at all other times is a proportion of the pressure signal which is dependent on the second engine operating parameter and also that, when the said input pressure is greater than the said second reference pressure the throttle valve is in an equilibrium position when the said first control pressure is equal to the said proportion of the input pressure.

2. A fuel control system as claimed in claim 1 in which the nozzle actuating means is operable to close the nozzle and comprises a single-acting piston and cylinder unit and valve means responsive to the said switching means to apply an actuating pressure tov the said single-acting piston and cylinder unit.

3. A fuel control system as claimed in claim 2 in which the said actuating pressure is derived from a pressure signal dependent on one of the engine operating parameters.

4. A fuel control system as claimed in claim 2 which includes latching means engageable with the nozzle actuating means to maintain the nozzle in its closed position and operable by a further actuating pressure to disengage from the nozzle actuating means, and means for deriving the said further actuating pressure from a pressure signal dependent on one of the engine operating parameters.

5. A fuel control system as claimed in claim 4 in which the means for deriving said further actuating pressure includes the said valve means responsive to the said switching means, and the arrangement is such that, in use, for any state of the switching means only one of the said actuating pressures is derived.

6. A fuel control system as claimed in claim 4 in which the said sensing means includes a fluidic control device actuable to derive a third actuating pressure from the said further actuating pressure.

7. A fuel control system as claimed in claim 6 in which the valve actuating means includes biasing means urging the shut-off valve to a closed position, a

servo piston operatively connected to the shut-off valve, means for admitting fuel under pressure to both sides of the servo piston and a servo valve operable in response to an increase in the said third actuating pressure to reduce the pressure applied to one of the sides of the servo piston so as to open the shut-off valve.

8. A fuel control system as claimed in claim 7 which includes a restricted by-pass for the throttle valve and in which fuel is admitted to the engine by the servo valve in response to the said increase in the third actuating pressure.

9. A fuel control system as claimed in claim 1 in which the means for generating the first reference pressure comprises a chamber having three restricted ports to which the pressure signals dependent of the second, third and fourth engine operating parameters are respectively applied, means responsive to the position of the throttle valve for varying flow through one of the ports, and an outlet port connected to said first fluid control means.

10. A fuel control system as claimed in claim 1 in which the said first and second fluid control means each comprises a first nozzle, an axially aligned recovery nozzle, a chamber within the first nozzle, the said chamber being formed so that its walls, viewed in the direction of the axis of the nozzles, include a pair of arcs, a first passage having an opening into the said chamber tangential to one of the said arcs and an oppositely directed second passage having an opening into the said chamber which is displaced from tangency to the other of the said arcs, the arrangement being such that only when the pressure of the fluid in the first passage exceeds that in the second passage by a predetermined amount will there be a tendency of the fluid to rotate about the axis of the chamber and thereby to emerge from the first nozzle as a substantially hollow cone and thus to reduce its reception at the second nozzle.

11. A fuel control system as claimed in claim 10 in which the first fluid control means has the input pressure dependent on the first engine operating condition applied to the said first passage thereof, the first reference pressure is applied to the second passage and the recovery nozzle is connected to the said one side of the double-acting piston and cylinder unit.

12. A fuel control system as claimed in claim 10 in which the second fluid control means has the input pressure dependent on the first engine operating condition applied to the second passage thereof, the second reference signal is applied to the first passage and the recovery noule is connected to the third fluid control means.

13. A fuel control system as claimed in claim 1 in which the means for generating the second reference pressure comprises a chamber having three restricted ports to which the pressure signals dependent on the second, third and fourth engine operating parameters are respectively applied, and an outlet port connected to said second fluid control means.

14. A fuel control system as claimed in claim 1 in which the third fluid control means comprises an element responsive to the second control pressure, a pair of aligned nozzles, a vane movable between the aligned nozzles by the pressure responsive element and a port communicating with a low pressure.

15. A fuel control system as claimed in claim 14 in which the aligned nozzles of the third fluid control means are respectively connected to the said other side of the double-acting piston and cylinder unit and to a pressure signal dependent on one of the engine operating parameters.

16. A fuel control system as claimed in claim 1 which 

1. A fuel control system for controlling the supply of fuel to burners of a reheat system of a gas turbine engine which includes a jet pipe nozzle movable between open and closed positions, the said fuel control system comprising a nozzle actuating means, a sensing means actuable when the nozzle is in its open position, a valve actuating means responsive to the sensing means, a shut-off valve for the fuel actuable by the valve actuating means, a throttle valve in series with the shut-off valve, a double-acting piston and cylinder unit for operating the throttle valve, a switching means operable when the throttle valve moves past a predetermined position to cause the nozzle actuating means to shut the nozzle, a first fluid control means for generating a first control pressure in accordance with the difference between a first reference pressure and an input pressure dependent on a first engine operating condition, the said first control pressure being applied to one side of the piston and cylinder unit, a second fluid control means for generating a second control signal only when the said input pressure is greater than a second reference pressure, a means for generating the first reference pressure in accordance with pressure signals dependent on second, third and fourth engine operating parameters and on the position of the throttle valve, a means for generating the second reference pressure in accordance with pressure signals dependent upon the second, third and fourth engine operating parameters, a third fluid control means responsive to the second control pressure and controlling the pressure applied to the other side of the piston and cylinder unit, the arrangement being such that when the said input pressure is greater than the said second reference pressure, the pressure applied to the said other side of the piston and cylinder unit is a proportion of the said input pressure, and at all other times is a proportion of the pressure signal which is dependent on the second engine operating parameter and also that, when the said input pressure is greater than the said second reference pressure the throttle valve is in an equilibrium position when the said first control pressure is equal to the said proportion of the input pressure.
 2. A fuel control system as claimed in claim 1 in which the nozzle actuating means is operable to close the nozzle and comprises a single-acting piston and cylinder unit and valve means responsive to the said switching means to apply an actuating pressure to the said single-acting piston and cylinder unit.
 3. A fuel control system as claimed in claim 2 in which the said actuating pressure is derived from a pressure signal dependent on one of the engine operating parameters.
 4. A fuel control system as claimed in claim 2 which includes latching means engageable with the nozzle actuating means to maintain the nozzle in its closed position and operable by a further actuating pressure to disengage from the nozzle actuating means, and means for deriving the said further actuating pressure from a pressure signal dependent on one of the engine operating parameters.
 5. A fuel control system as claimed in claim 4 in which the means for deriving said further actuating pressure includes the said valve means responsive to the said switching means, and the arrangement is such that, in use, for any state of the switching means only one of the said actuating pressures is derived.
 6. A fuel control system as claimed in claim 4 in which the said sensing means includes a fluidic control device actuable to derive a third actuating pressure from the said further actuating pressure.
 7. A fuel control system as claimed in claim 6 in which the valve actuating means includes biasing means urging the shut-off valve to a closed position, a servo piston operatively connected to the shut-off valve, means for admitting fuel under pressure to both sides of the servo piston and a servo valve operable in response to an increase in the said third actuating pressure to reduce the pressure applied to one of the sides of the servo piston so as to open the shut-off valve.
 8. A fuel control system as claimed in claim 7 which includes a restricted by-pass for the throttle valve and in which fuel is admitted to the engine by the servo valve in response to the said increase in the third actuating pressure.
 9. A fuel control system as claimed in claim 1 in which the means for generating the first reference pressure comprises a chamber having three restricted ports to which the pressure signals dependent of the second, third and fourth engine operating parameters are respectively applied, means responsive to the position of the throttle valve for varying flow through one of the ports, and an outlet port connected to said first fluid control means.
 10. A fuel control system as claimed in claim 1 in which the said first and second fluid control means each comprises a first nozzle, an axially aligned recovery nozzle, a chamber within thE first nozzle, the said chamber being formed so that its walls, viewed in the direction of the axis of the nozzles, include a pair of arcs, a first passage having an opening into the said chamber tangential to one of the said arcs and an oppositely directed second passage having an opening into the said chamber which is displaced from tangency to the other of the said arcs, the arrangement being such that only when the pressure of the fluid in the first passage exceeds that in the second passage by a predetermined amount will there be a tendency of the fluid to rotate about the axis of the chamber and thereby to emerge from the first nozzle as a substantially hollow cone and thus to reduce its reception at the second nozzle.
 11. A fuel control system as claimed in claim 10 in which the first fluid control means has the input pressure dependent on the first engine operating condition applied to the said first passage thereof, the first reference pressure is applied to the second passage and the recovery nozzle is connected to the said one side of the double-acting piston and cylinder unit.
 12. A fuel control system as claimed in claim 10 in which the second fluid control means has the input pressure dependent on the first engine operating condition applied to the second passage thereof, the second reference signal is applied to the first passage and the recovery nozzle is connected to the third fluid control means.
 13. A fuel control system as claimed in claim 1 in which the means for generating the second reference pressure comprises a chamber having three restricted ports to which the pressure signals dependent on the second, third and fourth engine operating parameters are respectively applied, and an outlet port connected to said second fluid control means.
 14. A fuel control system as claimed in claim 1 in which the third fluid control means comprises an element responsive to the second control pressure, a pair of aligned nozzles, a vane movable between the aligned nozzles by the pressure responsive element and a port communicating with a low pressure.
 15. A fuel control system as claimed in claim 14 in which the aligned nozzles of the third fluid control means are respectively connected to the said other side of the double-acting piston and cylinder unit and to a pressure signal dependent on one of the engine operating parameters.
 16. A fuel control system as claimed in claim 1 which includes a fluid flow restrictor through which the said input pressure dependent on the first engine operating condition is applied to the said other side of the double-acting piston and cylinder unit.
 17. A fuel control system as claimed in claim 1 which includes a pressurizing valve downstream of the shut-off valve, the said pressurizing valve having a pair of outlet ports respectively connected to burners of the reheat system, and operable in response to an increase in the pressure of fuel successively to uncover the said ports. 